This invention relates to modified polyamines containing urethane and/or urea and/or thiourethane groups and a process for their production.
It is known that aromatic isocyanates can be converted into primary aromatic amines by acid hydrolysis. However, the conversion is less than complete because the amine formed during hydrolysis further reacts with unreacted isocyanate to form the corresponding urea. This further reaction cannot be suppressed even by using excess strong mineral acid. A fairly recent example of such a process is found in Japanese Patent No. 55 007-827.
German Auslegeschrift No. 1,270,046 describes a process for the production of defined, primary aromatic amines containing polyalkylene glycol ether segments in which reaction products of aromatic diisocyanates or triisocyanates with polyalkylene glycol ethers and/or polyalkylene glycol thioethers (preferably those having molecular weights of from 400 to 4000) are reacted with secondary or tertiary carbinols. The products of this reaction are subsequently subjected to thermal decomposition at elevated temperatures in an inert solvent (optionally in the presence of acid catalysts). Apart from the high decomposition temperature, the disadvantage of this procedure is that flammable, readily volatile alkenes which are explosive in air are formed so that safety measures must be taken. Additionally, the loss of the tert-carbinol component makes the process undesirable from an economic standpoint.
German Auslegeschrift No. 694,152 describes a process for the production of prepolymers containing at least two terminal amino groups in which hydrazine, aminophenyl ethylamine or another diamine is reacted with an NCO-prepolymer of a polyether polyol and polyisocyanate (NCO:NH-ratio=1:1.5 to 1:5). Unreacted amine must be carefully removed in another step because the amine catalyzes the reaction with polyisocyanates thereby shortening processing times significantly.
Another synthesis for polyamines containing urethane groups is described in U.S. Pat. No. 3,385,829. In this disclosed process, NCO-prepolymers containing urethane groups are converted with formic acid into the N-formyl derivatives which are subsequently hydrolyzed to form terminal aromatic amines. The reaction of NCO-prepolymers with sulfamic acid disclosed in German Auslegeschrift No. 1,155,907 yields compounds containing terminal amino groups. Relatively high molecular weight prepolymers containing aliphatic secondary and primary amino groups may also be obtained according to German Auslegeschrift No. 1,215,373 by reacting relatively high molecular weight hydroxyl compounds with ammonia under pressure at elevated temperature in the presence of catalysts. U.S. Pat. No. 3,044,989 teaches that such compounds may be made by reacting relatively high molecular weight polyhydroxyl compounds with acrylonitrile, followed by catalytic hydrogenation. Relatively high molecular weight compounds containing terminal amino groups and urethane groups may also be obtained by reacting NCO-prepolymers with enamines, aldimines or ketimines containing hydroxyl groups, followed by hydrolysis (German Offenlegungsschrift No. 2,546,536 and U.S. Pat. No. 3,865,791).
Another approach to synthesizing aromatic polyamines containing urethane and ether groups is the opening of the ring which occurs in the reaction of isatoic acid anhydride and diols. Polyamines of this type are described, for example, in U.S. Pat. No. 4,180,644 and in German Offenlegungsschriften Nos. 2,019,432; 2,619,840; 2,648,774 and 2,648,825. The poor reactivity of the aromatic ester amines obtained in this way is a disadvantage in most applications.
The reaction of nitroaryl isocyanates with polyols, followed by reduction of the nitro groups to aromatic amino groups, is also known (U.S. Pat. No. 2,888,439). The main disadvantage of this process is the high cost of the reduction step.
It is also known that certain heteroaromatic isocyanic acid esters can be converted into heteroaromatic amines by basic hydrolysis. Unfortunately, the hydrolysis conditions described by H. John in J. Prakt. Chemie 130, 314 et seq and 332 et seq (1931) for two specific, heteroaromatic monoisocyanic acid esters are not only totally unsuitable for the conversion of poly-NCO-compounds into aliphatic and/or aromatic amines, they are also dangerous.
The subject of one of our own proposals (see German Offenlegungsschrift No. 2,948,419) is a multistage process for the production of polyamines by the aqueousalkaline hydrolysis of NCO-prepolymers with excess base, optionally in the presence of inert solvents, to form carbamates. These carbamates are treated with a quantity of mineral acid exceeding the quantity of base in order to decompose the carbamates. Excess acid is neutralized with a base and the polyamines are isolated by phase separation or extraction.
Our own unpublished German Patent Application No. P 30 39 600 describes alkaline hydrolysis in mixtures of water and monofunctional alcohols to form carbamates which are subsequently treated with ion exchange resins instead of mineral acids.
Although the latter two processes represent improvements over the prior art in many respects, there is still room for improvement. New products having improved properties obtained by modification of the polyamines are desirable for many reasons. More particularly, polyamines readily form ureas (through "H.sub.2 O-extension") instead of carbamates. This urea formation occurs particularly where the NCO:OH.sup..crclbar. -ratio is in the range from 1.01:1 to 1.2:1. Consequently the products form from compounds which were pre-extended through urea groups. Although the resulting polyamines containing urea groups are valuable for certain applications, a product free from urea groups is generally preferred for reasons of processibility. It would therefore be advantageous to have modified polyamines which will yield a product containing virtually no urea groups. NCO-prepolymers and other NCO-compounds of the type formed for example by reacting NCO-compounds themselves ("dimers" and "trimers") or with polyisocyanates containing urea groups (biurets) etc., usually contain a certain amount of monomeric isocyanate. This monomeric isocyanate is converted into monomeric polyamine (such as tolylene diamine) in our processes described above. For many applications, however, it is necessary or desirable that substantially no free low molecular weight amines be present for physiological reasons and also for reasons of reactivity. Elimination of such free low molecular weight amines may be achieved by subjecting the NCO-compounds containing low molecular weight polyisocyanates to distillation, optionally in vacuo, (for example using a so-called thin-layer evaporator) to remove the diisocyanates. However, this distillation step is rather expensive.
Another way of achieving substantial freedom from monomers is to add monofunctional or polyfunctional hydroxyl compounds after production of the NCO-prepolymer. However, this lengthens the residence time in the reaction vessel and increases costs.
Another problem encountered in the prior art processes is attributable to the fact that for many applications, polyamines containing terminal amino groups of the type obtained by the processes described above are preferably used in admixture with other polyamines containing terminal amino groups (such as aminopolyethers). Such mixtures may, for example, consist of an aminopolyether having a molecular weight in the range from 2000 to 4000 and an aminopolyether having a molecular weight in the range from 300 to 2000. Mixtures of this type may be prepared by mixing two or more of these polyamines with one another if the two polyamines are miscible with and soluble in one another. Such is not always the case, however. In addition, it is economically undesirable to attempt to carry out exactly the same process steps in order to produce one and the same reaction component. Such polyamine mixtures may also be produced by converting mixtures of NCO-prepolymers. In this case, two NCO-prepolymers have to be produced, in addition to which the solubility of the often solid, crystalline NCO-component having the lower molecular weight presents problems.
Polyamine mixtures may also be produced by adding a more NCO-reactive component to a semi-prepolymer which reacts with the excess monomeric polyisocyanate and then reacting the resulting prepolymer mixture with a hydroxyl compound. The disadvantages of this process include the need for a second step and the poor solubility of low molecular weight NCO-prepolymers in the relatively high molecular weight NCO-prepolymers. Crystalline deposit of low molecular weight NCO-prepolymers may be avoided by adding more NCO-reactive component to a relatively high molecular weight NCO-prepolymer so that pre-extension occurs. Apart from the fact that a second reaction step is again necessary, the viscosity of the pre-extended NCO-prepolymer increases. This is a disadvantage to processes such as those described above, which require as low-viscosity an NCO-component as possible, and makes it necessary to use a solvent.
If the alkaline NCO-hydrolysis is carried out in the presence of monofunctional alcohols (in accordance with unpublished German Patent Application No. P 30 39 600), a chain-terminating reaction may occur through the formation of a urethane group, depending upon the NCO- and alcohol-reactivity and the reaction conditions. This is undesirable in most cases.